A singulation procedure is typically performed to separate integrated circuit packages such as IC chips from a substrate such as a carrier or circuit board. During singulation, the substrate is typically held in place while one or more saw blades cut straight lines through the substrate in order to form the individual integrated circuit packages. This is sometimes referred to as “dicing.”
FIG. 1 is an exemplary diagram of a conventional dicing apparatus 2. The dicing apparatus 2 includes a fixture 4 for holding the substrate 6 during a dicing procedure, and a saw assembly 8 for performing the dicing procedure. The saw assembly 8 typically includes a rotating cutting blade 10 that is translated through the substrate 6 in order to cut parts therefrom. The cutting blade 10 is typically attached to a spindle 12 that rotates via a motor (not shown). Spacers may be provided on the spindle 12 between blades if more than one blade is used. Furthermore, in order to cool the blade 10 during the dicing procedure the saw assembly 8 may include a spray nozzle 16 that is spaced apart from the cutting blade 10. The spray nozzle 16 produces a stream of fluid 18 that is directed at the leading edge 20 of the cutting blade 10 near the cutting surface.
Although saw singulation works well, continuing advancements in the industry have tested the limitations of saw singulation. For example, Quad Flat No Lead (QFN) packages, which are one of the most cutting edge packaging technologies to recently emerge in the electronic marketplace, have been stifled by the inability of saw singulation to deliver effective results. In QFN, the dicing process may suffer from blade breakage, cut quality failures, part movement, low feed speed, short blade life and low throughput. The is due in part to the configuration of QFN packages, which are small and which include copper leads, and a mold compound through which the saw blade must cut in order to singulate the individual QFN packages from the substrate.
To elaborate, one problem with the current dicing process is that scrap material may be thrown into the blade or become trapped between the blade and portions of the fixture and this may cause blade breakage or poor cut quality. Another problem with the dicing process is that the feed rates are kept low to prevent excessive blade wear and poor cut quality (e.g., chips, burrs). For example, QFN singulation typically requires specially formulated blades that must constantly expose new diamonds to the cut interface. As the diamonds remove material, they are “dulled” by the materials used in the substrate and must be sloughed-off as the blade wears at a higher-than-normal rate. The balance between blade wear and cut quality is a delicate trade-off requiring costly technology to extend blade life while minimizing burrs and chips.
Another problem with the dicing process is that the substrate and parts cut therefrom may move during the cutting process. As should be appreciated, the saw blade(s) is both rotating and translating relative to the device under process. The resulting force vectors have both vertical and shear components, which can overwhelm the holding force of the fixture thereby causing part movement. As feed rates increase, the magnitude of the shear component increases commensurately and magnifies the device retention problem. As a result of this movement, non conforming geometries, damage and lost parts may be created. Even if the parts do not move, the shearing forces created by the cutting blade may cause the copper leads to smear thereby creating non conforming parts.
Another problem with the dicing process is that the blades can become imbalanced, and imbalanced blades can cause blade breakage, excessive blade wear and poor cut quality. By way of example, the blade(s) may become imbalanced by spacers located on the sides of the blade. The imbalance may be caused by fluid accumulation inside or around the spacers. As shown in FIGS. 2A and 2B, spacers 22 consist of an annular member 23 having an inner radius 24 that fits around the spindle 12 and an outer radius 26 including a raised surface 28 extending from its side that presses against the side of the blade 10. As shown in FIG. 2C, the spacers 22 are designed to only contact the blades 10 along their raised surfaces 28, thus leaving a gap or cavity 30. Unfortunately, during the dicing process, the fluid used in the dicing process (e.g., fluid stream 20) tends to accumulate in this gap 30 thereby creating imbalance problems when the blades 10 are rotated via the spindle 12.
In view of the foregoing, it would be desirable to provide improved systems and methods for dicing a substrate into a plurality of integrated circuit packages.